The present invention relates to transferring image data for use by image processing systems.
Video post production techniques are known in which digital signals representing images are manipulated in a process generally referred to as compositing. Video data is stored on magnetic tapes such as D1 broadcast quality component tape, transferred into a compositing environment, composited and edited etc., and then recorded back on to digital video tapes. As is known in the art, an advantage of transferring data digitally is that many repeated operations may take place or many layers of video may be combined. Ultimately, a final output tape is produced from which broadcastable material may be derived.
Such a compositing environment will typically be based on an image processing workstation running a compositing software application. A variety of such hardware and software applications are available having varying capabilities and prices. In general, the more expensive the hardware or software package, the greater its processing power. The lower power, less expensive workstations may not be able to process video data at a speed sufficient to provide real time previewing of the results of image compositing. This means that there is a delay between performing the compositing operation and viewing the outcome.
One possible solution would be to include routines within the compositing software application which attempt to provide real time previewing facilities. This, however, would require the application software to be re-written which is expensive in terms of design and implementation time. This would also require the users of the software application to purchase the new upgrade or a completely new software package.
According to a first aspect of the present invention, there is provided a method of transferring image data describing sequences of images representing a plurality of clips from a storage device to a high speed memory for image processing, comprising the steps of: predicting image data which will be required by said image processing step after processing image data currently in said high speed memory; and transferring said predicted image data from said storage device to said high speed memory while processing said current image data.
Preferably, the predicting step includes creating a look-ahead map having data describing said plurality of video clips; creating a history table of requested images; and searching for patterns in said look-ahead map and said history table to predict images which will be required by said image process. Preferably, the indications of said predicted images are stored in a prediction table and the data describing each image in said look-ahead table may comprise physical storage addresses on said storage device of the next image in a clip.
According to a second aspect of the present invention, there is provided image data transfer apparatus, comprising processing means including a processor executing one or more image processing applications, a high speed memory and a storage device, wherein said processor is arranged to transfer image data describing sequences of image representing a plurality of clips from said storage device to said high speed memory by predicting image data which will be required by said image processing applications after processing video data currently in said high speed memory; and transferring said predicted image data from said storage device to said high speed memory while processing said current image data.
In a preferred embodiment, the processor is arranged to perform the prediction and transferring of predicted image data each time image data is requested from said storage device.